[culver]

Mantra, this conversation has become very interesting!
I’m sure much of what we are debaiting is like two people trying to describe the exact same thing. It’s a red car! No, it’s a sports car!


First, from what I have heard from the people I know in race car design (Formula Ford – Infinity Pro Series cars) they have never said anything about harmonic issues when they looked at Vette suspensions. On guy I know is trying to get the company that does the Vette springs to make landing gear springs for tail dragger airplanes.
Again, no one I know in the racing industry sees a problem with harmonics in the Vette’s design.
Has anyone reported this as a problem or is this assessment based on intuition. I ask simply because I’ve never heard this issue before.

OK, a couple of replies:

no, it works in an entirely differnet fashion.
An anti-roll bar is NOT restrained at the mountinf points, so when one suspension wheel moves up the bar is twistsed ADN TURNS IN THE MOUNTINGS to impart a force to the other side. Yes there is still a harmonic issue but NOW it is at wavelength harmonics of the length of the COMPLETE bar. And as it is NOT require to act as a sprign it is usually torsinoally VERY stiff and hence very HIGH natural frequency beyond the expected movements - because you are loking at the rate of change BETWEEN the wheels NOT between wheel and chassis.

The 'vette spring issue is that it's harmonics are at a much shorter wavelenght/higher rate.
The spring does not TWIST it bends, the bend is perpendicular to the mounting points, so it's not imparting directly to the other side.
As a wheel drops, the INNER section of the spring will go UP, hence imparting a downward force to the other side. So it performs TWO functions.

I understand how the conventional anti-roll bar twists instead of flexes. However, you can get torsional harmonics as well as flexing harmonics. I also agree that the natural frequency of the beam makes it unlikely to be much of an issue.
I’m not sure I understand your second point. I think you are saying that when one wheel goes up it tends to pull the other wheel up as well. If that is what you are saying, I would counter that this is intentional. As was mentioned in one of my original links, this was an intentional design trait of the C4-C6 leaf spring suspensions. This is exactly how the leaf spring can handle two jobs at once. The roll spring rate of the Vette is provided by a combination of the leaf spring and the anti-roll bar. I’m not sure why this would be considered undesirable. Certainly unconventional but hardly undesirable.

good point on it being composite, but I can't see how they can build in a DAMPING property for bend, vibration yeah, sure, but bend ?? Because IF they build it in to supres the natural frequency AND it's hamronics then you NOW have it doing 3 jobs at the rear - anti-roll, spring AND damper. I jsut dont' see that being controllabel to have a reasonably wide range of handling for differing surfaces.
Again, I’m not sure if I understand the damping property for bending. I think I’m unsure how much vibration you are talking about. If we are talking about macroscopic levels that start moving the wheels around then I will reiterate, I don’t think the problem exists in the first place. Sorry if I’m still not understanding the issue you are concerned with.

erm, that might be true for something like an oval where suspension transitions are gentler. BUT there is NO WAY a suspension is designed around 1"/sec velocities for a road cricuit
Do you have a link as I'd like to check up on that one as I'm very surprised by it. Maybe we are talking different velocities.
This one is easy, link below. The presentation in the link was put together by a 7 time SCCA national champion driver. He is a senior engineer at Firestone and also happens to be his own race engineer. While he has done some oval stuff most of his driving is on road courses (ovals may look easy but they also take a great deal of skill to squeeze out that last 0.02 seconds). Remember, I didn’t say that was the only frequency in the suspension’s motion, just that is was considered to be the most critical.
http://www.neohio-scca.org/comp_clin...handout%20.pdf

As for my third point, I’m not actually sure exactly what material they use as an interface between the spring and chassis. In the pictures it’s black. I assume it’s somewhat compliant. I’m not talking about the ends of the spring were it attaches to the suspension arms, I’m taking about the clamps that hold the spring to the sub-frames. Even at the wheel ends I imagine there is some sort of rubber layer in between the spring ends and the suspension arms. From the pictures it looks kind of like a, for lack of a better description, a bolt with rubber washers. Remember, the spring mounts at the wheels will always be in tension so a semi-compliant peace like a rubber washer will be under compression the whole time. This is different that say a suspension bushing that will transition from compression to tension under different loading conditions. I also do not know how much compliance we are talking about but having ridden in a Vette, I imagine it’s quite small. Again, I think the issue we are having is one of communication rather than facts. The illustration seems to show an A-arm pivot which is not what I’m referring to. I’m referring to the connection between the end of the leaf spring and the suspension arm. The Vette’s suspension arms and thus it’s suspension geometry are very carefully mounted and controlled.
Hopefully this first post will show what I’m talking about:
http://www.z06vette.com/forums/showt...5&page=2&pp=27
Note what appears to be a semi-compliant mount between the A-arm and the end of the spring. Since this joint is under constant tension I would expect it uses some sort of rubber bushing. This is not an A-arm pivot point. Those look rather conventional. You can also just see a bit of what ever compliant material they use to mount the spring to the chassis in the upper left of the picture.